- Distribution

Present Distribution

Today giants sequoia grow and reproduce naturally
only in scattered sites along the western slope
of the Sierra Nevada. These sites are all within
a 260 mile long zone at elevations between 4,000
and 8,400 feet. Even in these widely scattered places
giant sequoia does not form pure stands as does
the coast redwood. Instead, it occurs sporadically,
scattered throughout a forest community made up
of sugar and ponderosa pine, white fir, and incense
cedar as well as a characteristic group of shrubs
and smaller plants.

The most northerly grove of giant sequoias is near
the middle fork of the American River in Placer
County. It consists of only six trees, and is of
particular interest because it is so small and so
widely separated from the other sequoia groves.
Recent reproduction seems to be extremely limited,
and the grove may well be struggling against adverse
environmental conditions. Toward the southern end
of the giant sequoia range - in the Kings, Kaweah,
and Tule River Basins - the trees are much more
numerous, and they occur throughout broad areas,
sometimes as few as two or three to an acre. South
of the Converse Basin the sequoias form an almost
continuous belt, with none of the groves being more
than five miles from its nearest neighbor. Nevertheless,
most observers continue to apply the grove concept
and identify a total of sixty-five or as many as
sixty-seven groves.

Past Distribution
As a species, giant sequoia has been traced as far
as the middle Miocene epoch of the Cenozoic era,
fifteen to eighteen million years ago. But the present-day
giant sequoia and other redwoods of the past and
present all belong to a family of trees - Taxodiaceae
- that probably had its origin in the Triassic period
of the Mesozoic era some 200 to 230 million years
ago.

By the beginning of the Cenozoic era, the "era of
recent life," some sixty-five million years ago,
the ancestors of our present-day redwoods were part
of an extremely diversified plant community that
was established in the middle and high latitudes
of the northern hemisphere. The forest trees of
this community included both conifers and deciduous
hardwoods, such as oak, birch, elm, chestnut, and
others. Among the conifers several redwood species
were especially abundant. As Asa Gray maintained
more than one hundred years ago, redwood-filled
forests did in fact extend into the arctic regions
in such places as Greenland, Iceland, Northern Siberia,
and even Spitzbergen and Ellesmere Island, both
of which are now located far to the north of the
Arctic Circle.

Several species of Sequoiadendron were present in
western Europe and in both western and eastern North
America. As with other redwoods, these Sequoiadendron
species were driven southward after the close of
the Paleocene and may well have disappeared from
Europe as early as the Oligocene or early Miocene
some twenty-five million years ago. In North America
a similar pattern of southward retreat and extinction
was followed until finally just one species of Sequoiadendron
remained. This was S. chaneyi, a tree that seems
to have been virtually identical to our present-day
giant sequoia.

As climatic conditions in Nevada and Idaho during
the Miocene become generally cooler and drier, there
was also a trend toward more extreme seasonal differences.
As rainfall decreased still further toward the middle
of the Pliocene, virtually all of west-central Nevada's
forest trees were restricted to stream and lake
borders, and then eliminated.

At this time, the mid-Pliocene, perhaps six to eight
million years ago, the Sierra Nevada was much lower
and had a warmer climate than at present. Geologists
are not in complete agreement about the timing of
Sierra Nevada uplift, but it now seems likely that
during the middle Pliocene the northern part of
the range stood at about one to two thousand feet
elevation while the central part of the range had
reached about three to four thousand feet. Once
the range had reached this elevation, and later,
toward the end of the Pliocene as it was lifted
still higher, it began to have an increasingly strong
influence on weather conditions - that is, its presence
began to bring about conditions that were favorable
to the development of a giant sequoia forest on
the west slope and unfavorable to the continued
survival of the older forest on the east. Giant
sequoia had completely disappeared everywhere except
on the Sierra Nevada's west slope by the time the
great Pleistocene Ice Age began, perhaps as little
as one million years ago.

In the Sierra Nevada, glacial activity seems to
have reached its maximum extent 25,000 to 50,000
years ago. We can not be certain what happened to
giant sequoias during this time. The most recent
glacial advance, the Wisconsin, has been identified
as the major reason for the present, widely separated
or discontinuous occurrence of giant sequoia groves.

John Muir theorized that giant sequoia had probably
once been widely and uniformly distributed along
the western slope of the Sierra. Its present highly
discontinuous distribution was due to its elimination
from those valleys down which glaciers had advanced.
Although his analysis of the impact of glaciation
on giant sequoia distribution is still accepted
in general, particularly for the northern half of
the Sierra where glaciation was more severe, other
climatic factors may have had a role in restricting
giant sequoias to their present grove areas.

Excerpted from "The Enduring Giants"
by Joseph H. Engbeck Jr., published by the California
State Parks.